Unlike indigenous amphibians that have adapted to arid conditions, the imported anuran desperately needs access to nearby standing water in order to survive.

Placing small fencing around irrigation ditches and troughs is enough to cause the toad to die of dehydration and stop its advance, says the study.

"Basically, step by step, toads use these water points to invade the drier regions of Australia," says University of Melbourne researcher Tim Dempster.

"By stopping toads from using these water points, we are removing their 'stepping stones' in the landscape."

Halting the invasion

Dempster's team experimented with cane toads which were placed near nine artificial water points during the dry season in the Victoria River District of the Northern Territory.

Some of the water points were unfenced, but others were surrounded by cloth netting 60 centimetres high that also extended along the ground to stop the large toads from burrowing underneath. The netting was secured by wire and metal posts at least two metres from the water's edge.

All 21 toads placed near fenced-off water points died, and most of them expired within 12 hours.

Of the 20 toads with unfettered access to water, all survived except for one, which was killed by a predatory bird.

Dempster says fencing off even a small number of key water points can halt further invasion and save a million square kilometres - an area larger than the state of New South Wales - out of the 2.24 million square kilometres of arid land threatened by the beasts.

"The greatest benefit from the technique will be to stop further invasion into several of Australia's drier inland areas which are hotspots of unique native animal biodiversity," Dempster says.

The method is feasible for water points that are around 20 metres across, but only key points would need be fenced for the barrier to be effective, he says.

Practical, but not an overall solution

Professor Ross Alford of James Cook University in Townsville says the study confirms earlier findings that restricting access to water limits the cane toad's ability to spread.

"But as the paper itself mentions, it probably will only be possible to do this for artificial dams, not for the many natural water bodies that also exist in semiarid regions," says Alford.

"Even if it were possible to fence off every natural waterhole, it would probably have severe negative impacts on many non-target species. There are also issues of cost and of what would happen during wet seasons.

"All in all, this approach may be practical and help to control toad numbers on some properties, but it seems unlikely to offer a solution to the overall problem of cane toads in semi-arid Australia."

B. Marinus already extends across 1.2 million square kilometres of Queensland and the Northern Territory and, advancing at up to 50 kilometres a year, is on course for eventually spreading around three-quarters of Australia's coastline, say some experts.

It has driven some native frogs and reptiles to near-extinction, inflicted catastrophic declines in snakes and crocodiles that snack on its flesh and decimated goannas, a native lizard that is also a staple food in Aboriginal communities.